E Van Royen

Cryopreservation as a tool to reduce multiple birth

The potential role of embryo cryopreservation from the point of view of prevention of multiple pregnancies is analysed. Cryopreservation is an unavoidable option in stimulated IVF/intracytoplasmic sperm injection (ICSI), but at the same time an underestimated tool in the prevention of twins. There is a need for an evaluation system not only of the cryotechnology process per se, but also of the true augmenting effect of cryopreservation on the total reproductive potential of a single oocyte harvest. Only cryopregnancies occurring after an unsuccessful fresh cycle (possibly followed by one or more unsuccessful freeze-thaw cycles with embryos from the same harvest) truly reflect the augmentation potential of cryopreservation. This potential is greater than generally thought. First, the efficacy of cryopreservation is suboptimal with survival rates between 30 and 70%. Second, if single-embryo transfer were applied in a much larger proportion of cycles than is presently the case, more embryos would be available for cryopreservation, resulting in more and more successful freeze-thaw cycles. In the future, the combination of elective single-embryo transfer with an optimized cryopreservation programme is likely to become the standard of care for routine IVF/ICSI treatment.

Impact of single embryo transfer on the overall and twin-pregnancy rates of an IVF/ICSI programme

This retrospective cohort study analyses experience with single embryo transfer (SET) in an lVF/intracytoplasmic sperm injection (ICSI) programme over a 3-year period (1998-2000): 1143 IVF/ICSI cycles were initiated, resulting in 1073 embryo transfers (93.9%). In 810 (75.4%) transfers of two (n = 580; 54%) or more than two (n = 230; 21.4%) embryos, 279 ongoing pregnancies (34.4%) were obtained. In total, there were 263 SET (24.5%): 207 of a single top quality embryo, resulting in 102 conceptions (49.3%) with 71 ongoing implantations (34.3%, one monozygotic twin); and 56 of a single non-top quality embryo, resulting in 16 conceptions (28.6%) with 11 ongoing implantations (19 .6% ). The percentage of transfers of a single top quality embryo gradually increased from 10% (1998) to 19% (1999) to 26% (2000). The total multiple pregnancy rate decreased from 34% (1998), to 32% ( 1999) and 22% (2000), without affecting the overall ongoing pregnancy rate per transfer: 38% in 1998; 29% in 1999; and 34% in 2000. The average number of transferred embryos decreased from 2.26 ( 1998) to 1.86 (2000). Transfer of a single, strictly defined top quality day 3 embryo in twin-prone IVF/ICSI patients reduced the multiple/twin-pregnancy rate but not the overall pregnancy rate.